Line a 9x13-inch baking dish with foil and lightly grease it.

In a large pot over medium heat, melt the butter. Stir in the salt and vanilla.

Add the marshmallows and stir until melted and smooth, about 5 to 7 minutes.

Remove from heat and fold in the Rice Krispies cereal until fully coated.

Transfer the mixture to the prepared pan.

With greased hands or rubber spatula, gently press into an even layer.

Let sit at room temperature for about 30 minutes, until firm.

Remove from the pan and place on a cutting board.

Melt the white chocolate in the microwave in 30-second intervals, stirring between each until smooth. Drizzle over the top, then add sprinkles and M&Ms.

Add another drizzle of white chocolate and a few more sprinkles for extra color.

Let set until hardened, then cut into squares and serve.